Inosine is a vital substance involved in chemical synthesis and enzyme catalyzed synthesis of 5′-inosinic acid, which has drawn much attention as a savory seasoning. In addition, inosine, which is an intermediate in a metabolic pathway for nucleic acid biosynthesis, plays a physiologically significant role in the bodies of animals and plants and has been widely used in various fields including food and medicines.
Inosine has been conventionally produced by fermentation using microorganisms such as Bacillus (Agric. Biol. Chem., 46, 2347 (1982); Korean Patent No. 27280) or Corynebacterium ammoniagenes (Agric. Biol. Chem., 42, 399 (1978)), or by thermal decomposition of 5′-inosinic acid (Japanese Patent Laid-Open Publication No. 43-3320). However, in the case of the thermal decomposition of 5′-inosinic acid, a large amount of heat is required to decompose 5′-inosinic acid, and thus it is difficult to practically use this method. In the case of the direct fermentation, various strains of E. coli have been developed and studied (Biosci Biotechnol Biochem. 2001 March; 65(3):570-8). However, the titer of inosine-producing strains is low, and thus the production costs of inosine are high. In addition, research on inosine production has focused on E. coli and Bacillus stains.
Thus, there is still a need to develop microorganism strains capable of producing inosine with a high yield and accumulating inosine at a high concentration, and a method of producing inosine using such strains.
Therefore, we continued to study a method of producing inosine with a high yield/concentration by concentration by direct fermentation using a microorganism, and as a result, for the present invention, developed a microorganism producing inosine with a high yield/high concentration.